As the capabilities of weapon systems increase there is a corresponding need to make military assets more difficult to detect. Naval ships, like aircraft, can benefit from stealth technologies which reduce infrared (IR) and radar signatures. IR signature reduction is typically addressed by cooling and masking techniques. Radar signature reduction is achieved by a combination of a shaping and coatings or absorbers. However, while aircraft weapon systems can be masked by placing them inside the fuselage, naval designers are challenged in that certain weapons systems, such as the main gun, are simply too massive to hide within the superstructure.
Conventional gun barrels have characteristics that make them relatively easy to detect by infrared (IR) sensors and by radar. Their long, cylindrical shape tends to create strong return signals when illuminated by radar from almost any axis. Further exacerbating the return signature is the multiple bounce effect of the barrel interacting with neighboring surfaces of the superstructure.
A number of factors can create a large IR contrast between a gun barrel and its background. The most formidable IR signature effect is due to the heating of the barrel from the propelling charge. Each time the gun is fired, the barrel is heated by friction due to contact between the shell and the rifled barrel as well as the explosive propellant charge. After repeated firing, the temperature of a barrel can reach levels of 500° to 800° Fahrenheit above that of the surrounding background. This large temperature rise is not limited to the rear portion of the barrel but continues to, and includes, the muzzle. Moreover, the large mass and thick walls of the gun barrel result in heat retention long after firing ceases. This severely limits the effectiveness of simply supplying an insulating media to the barrel.
Barrel signature reduction methods must be compatible with the challenging operating conditions experienced by the gun. Firing a projectile subjects a gun barrel and the shroud to high recoil accelerations in excess of 100 Gs. Furthermore, the axial displacement of the gun barrel during the recoil cycle must be accounted for when attaching a shroud. The gun barrel recoil mechanism allows the barrel to recoil into the gun mount. A fixed rigid shroud encompassing the length of the barrel must be designed to accommodate barrel travel during recoil.
Firing the gun produces an additional design constraint at the muzzle end of the barrel. A shroud must account for a shock wave known as “muzzle blast” upon exit of the projectile. The shock wave is detrimental to any structure forward or transverse of the barrel muzzle. The muzzle blast effect is further complicated by the fact that the gun barrel begins to recoil prior to the exit of the projectile and continues to move rearward during the generation of a muzzle blast. If this movement is not correctly accounted for in the design of the shroud, the potential exists to expose elements of the shroud to the large pressures of the muzzle blast.
Most gun mounts must also be capable of moving the barrel in multiple axes to allow aiming of the gun at a wide range of target positions. The weight and inertia of the gun barrel and its associated hardware predominantly determines the size of the power drives required to aim a gun mount. It is paramount that weight and inertia of the shroud be minimized so as not to adversely effect operation of the gun.
U.S. Pat. Nos. 4,638,713, 4,753,154, 4,982,648, 5,062,346, and 6,314,857 describe various means of thermal reduction systems for gun barrels. For example, U.S. Pat. No. 4,753,154 describes a system in which the gun barrel is surrounded by a cylinder containing a working fluid. Other cooling systems involve air and insulation materials. Such solutions focus more on barrel cooling for maintaining rates of fire as compared to reducing thermal signatures. Furthermore, these designs do not address a reduction in the radar signature.
U.S. Pat. No. 5,400,691 describes a sleeve for a tank barrel which provides radar and IR signature reduction. An air gap is created between the barrel and inner sleeve of the device. The single piece rigid sleeve is of a honeycomb or foam construction. The air gap is sealed at opposing ends of the sleeve by a silicon ring which is intended to absorb the recoil energy. The solution does not address or alleviate the heating created by advanced guns capable of high rates of sustained fire. Furthermore, the rubber rings cannot absorb the recoil energy associated with large caliber weapons where firing results in recoil travel of more than one foot.
In summary, to enhance survivability of a gun system, there is a need to provide a shroud for a gun barrel providing a combination of radar and IR signature reduction. The shroud must be capable of reducing the heat signature created due to repeated firing of the gun. The exterior of the shroud must be dimensioned and fabricated so as to eliminate or at least reduce radar backscatter. Further, the shroud must conceal the entire length of the barrel both before and during displacement created by the recoil. Finally, the shroud must have minimal weight and inertia so as not to adversely impact the primary function of pointing the gun barrel at the target.